Bombsight



Nov. 7, 1950 I P. M. s. BLACKEVTT, ETAL 2,529,324

BOMBSIGHT Filed Nov. 1, 1943 6 Sheets-Sheet 1 I Q F/GZ. 9v

COURSE SET AUTOMATIC TSR gET cm spz WW0 AIR SSE-fil S gma? BY HAND R SPEED R PRESSURE sET wmo SPEED HEIGHT 522:? ABOVE v TARGET l l .L IDEAL BOMBING ANGLE IN LEvEL FLIGHT AUTOMATiC GLIDE OR CLIMB DRIFT BOMBING ANGLE ANGLE Attorney O 7, 1950 P. M. s. BLACKETT, ET AL 2,529,324

BOMBSIGHT 6 Sheets-Sheet 2 F/GZ. 3

ELECTR/C MOTOR Ram-bk M Ingeniou- JW 2& 6%

Attorney Nov. 7, 1950 P. M. s. BLACKETT, ETAL 2,529,324

BOMBSIGHT Filed Nov. 1, 1943 6 Sheets-Sheet 5 P 6 i n uentors MM By Nov. 7, 1950 I P. M. s. BLACKETT, ET AL 2,529,324

' BOMBSIGHT Filed Nov. 1, 19 1s s Sheets-Sheet 4 ,DDDDDDDW 31) I Inventors M7 jo-Lu By 64,441,} /a

Atlorney Nov. 7,1950 PQM. SfBLACKETT, ETAL 2,529,324

BOMBSIGHT Filed NOV. 1, 1943 6 Sheets-Sheet 5 tors I In WWT Attorney 7, 1950 I P. M. s. BLACKETT, ETAL 2,529,324

BOMBSIGHT Filed NOV. 1, 1943 6 Sheets-Sheet 6 AIRCRAFT couRsE POINT oE AIRCRAFT POSITION RELEASE AT TIME OF IMPACT soMmc\ ANGLE BOMB TRAJECTOIY FIG. 7 6}G\ -TRA\L GROUND LEVEL TARGET m G/ E \q, a

FIG. o 30L P- E {q DRIFT v ANGLE n w I TRACK or AIRCRAFT. GROUND SPEED VECTOR FIG. 9'

MoTon MOTOR Patented Nov. 7, 19.50

umrao STATES? PATENT OFFICE! BOMBSIGHI:

PatrickMaynard-l Stuart Blackett, Pitcullen, Bin-- nerr Hall, and Henry John James Braddick, Farnborough, England, assignors to thevMine ister of Supply, in His Majestysfiovernment of. theiUnited, Kingdom of Great" Britain and Northernlrel'andlIiondon, England Application November; 1, 1943, Serial No. 508,652: In Great'Britain Deoemberfil, 19,41

Seotionl, .Public Law 690;- AugustLS; 19.46

I Patent exDiressDecember 31,, 19.61,

1, The; invention. relates; to bombsights for aircraft:

When1a bombor theglike projectile isreleased from an aircraft, the. initial" forward velocity of" the bomb'relative toa fixed pointis the same as that of" the, aircraft; and its. downward velocity zero; If the bomb were falling in'vacuo, its.for

wardvelocity would be constant and it would". undergo downward acceleration due to gravity, and; assuming, that'the heightand ground speed, of; the aircraft were maintained constant, the

trajectory," of thebomb would" be-a curve of increasing steepnessbeingof such form that. at any instant during; its fall the bomb wouldbe vertically below the position of the aircraft, at

that instant. A straightline drawnbetween the pointof release ofthe projectile and the'point of impact of the projectile, said'line'constituting thev sighting; line, would. makejjan' angle with the horizontal termed ideal, bombing angle, the. value of'which wouldidependionthe height; of"

the aircraft, above the point of. impact, and. on

the'ground' speed of the aircraft, i; e. the speed of the aircraft relative to the point-of impact; In. practice however the forward motion of the bomb is d'ecelerated Owing to wind resistance andthe bomb lags behind'the aircraft, the amount of such lag at'the' point ofimpact; beingdesignated *trail. The ideal bombing angle must therefore be correctedff'or trail'to give anactual' bombing angle, andthe bombingangle is also subjectto further correction, if; the aircraft is not flyin level; i. e. forv the. pitch attitude of the aircraft, to obtain a' sighting angle defining, the

sighting line in relation to a datum line in the aircraft;

If the aircraft is not flying directly up or down wind, the trackof theaircraftwill; deviate from the heading of the aircraft, and the angle between aircraft heading and traclris" designated drift angle. Since the bomb after release will-travel in the same direction asthe aircraft; the sighting line must be rotated through an angle the magnitude of" which depends, on the. drift. angle. The

geometrical relationbetween th points referred.

to is illustrated in Figs. 'TandBof the accompanylllg drawings.

An object ofjthe invention is to produce a bombsight. comprising a mechanical, computer from whichthe .sighting and idriftangles are con-.

tinuously obtainable and a sighting arrangement defining a sighting line, which is, automatically adjusted by variations in. the. sighting angle and.

drift anglenbtained fromlthe computer...

In a computer for a bombsi'ght in accordance 4-Claimsz (01. 33-465) with theinvention, means .are provided for computing drift angle, and ground speedfrom the course ofthe; aircraft, the direction and-speed of the wind; and" the airspeed relative tOlDhGHlf-i craft; means for computing an ideal bombing angle: as hereinbeforer defined from the ground speed" value 'so; obtained and" theheight of the?- aircraft above the target, means. for applying a trail correction'to saididealjbombing angle, said' trail correctionbeing computed for the airspeed and-the ballistic properties oftheprojectile, and; means for applying-a further correction to said idealbombing angle in response to changes in pitch attitude of the aircraft, whereby the value, of" the sighting angle isobtained. The values continuously obtained from such a computer are transferred continuously to: a sighting arrangement whichdefines-a sightingline, so as to move the sighting line inaccordance with;the indica tions of sightingangle anddrift angle obtained from the computer;, Since the bombing angle 'is defined in relation to the horizontal, whilethe sighting angle is relatedto a datum lineinthe aircraft, the bombsightiorra partthereof musi'rbe-v stabilised ini roll, sothat the" datum lineis maintained steady in" azimuth during bank-ed turns;- 01" similar motion involvinga change in roll attitude" 7 and, 8 arevect'or diagrams illustrating the geo-.

' metricalprinciples,involvedpand Fig. 9 is a circuit diagram.

Referring to Eig.,,l,th dat Wh chin h p ferred embodiment, shown: in i Figs. 2-5 are, supplied manually to. the, computer re nclose in circles, those which are supplied automatically to the computer are..enclpsediimrectangles drawn in light 1ines, andthose which are automatically computediby, the computer areenclosediin recv tangles drawn in heavy lines. The figure thus shows that. the course, airspeed and height are automatically supplieditoth computer, the air. pressure at sea level, target height, wind direction, wind speed, andterminal velocity of" the projectile, (T.,V .,in .the figure), are preset manually, andthat from these data thedrift anglagroundf speed and height above t'arget'are computedautois derived from two electric motors I and 2."

Pneumatic detector systems are also provided,

and compressed air for these is obtained from a pipe line 3, equipped with a pressure reducing valve 4. A pressure-actuated switch -is also located in the motor supply circpit,so that the-cura spindle 2I is a blade 26. Increasing altitude with consequent fall in atmospheric pressure will cause the bellows. .I8 to collapse and the bellows I 9.to;expand thus rocking "the; links'a23 'and 24 and causing the free end of the blade 26 to rise while decreasing altitude will cause the free end or the blade 26 to fall.

The blade 26 forms the detector of an electro-pneumatic servo system rent supply to the motors land 2 is interrupted if the pressure in the pipe line 3 falls below a a predetermined lower limit.- The circuit and switch are diagrammatically illustrated in Fig. 9. For convenience in reading, further description of the computer is arranged under headings.

Manual settings The target height is preset on the computer, by rotating the knob I0, secured to a'shaft II, which causes through gearing I2, I3, a dial I4 to rotate, the dial I4 being juxtaposed with a stationary dial I5 which is engraved'with indications of barometric pressure for the sea level pressure at the location of the target. A pointer I6 is attached to a knob ITI, enabling the value for the sea level barometric pressure at the location of the target to be preset by rotating the knob 11, after which the knob I 0 is rotated until the value on the. dial I4 oppositethe pointer I6 corresponds with the known or estimated height above sea level of the target. Rotation of the knob I0 also adjusts the height'mechanism to be de scribed hereinafter.

Wind direction is set by rotation of the knob I00 for the known or estimated wind direction is op posite a fixed pointer I08, and rotation of the knob I04 is continued until the reading on the dial I01 appropriate for the known or estimated wind speed is opposite a fixed pointer I09. Rotation of the knobs I00 and I04 also adjusts the wind mechanism to be described hereinafter.

The known value of the terminal velocity of the bomb or class of bomb which is to be dropped is preset on the mechanism by rotation of a knob 260, fast with a shaft 26I carrying gearing 262, causing a dial 203 to rotate, until the appropriate value engraved on the face thereof is located opposite a pointer 264. Rotation of the knob 260 also adjusts the trail mechanism to be described hereinafter. The terminal velocityof a'bomb is that velocity at which the acceleration due to gravity just equals the retardation due to air resistance, i. e. the maximum downward velocity attainable when falling through air.

Height mechanism The height mechanismof the computer comprises a bellows I8, the interior of which is connected to aeroplane static pressure, and a bellows I9 the interior of which is exhausted. The bellows I8 and I9 are mounted at one end onropposite ends of a base plate 20, and are attached at their other ends to frames 2| and 22 secured to a pair of rocking levers 23 and 24 fast on a spindle 25 i pivoted in lugs on the base plate 20. Fastwith for which power is derived from the motor I.

Driven by the motor I is a shaft carrying two friction discs 21. 28,- between which is located a friction ring 29 carried by a shaft 30 having a flexible coupling 3I. The friction ring 29 is moved into contact with the disc 21 by expansion of a bellows 32 against the action of a spring 33, while when the'bellows collapses the spring 33 moves the friction'ring into contact with the disc 28. Air under pressure is supplied to the bellows 32 through a .branch 34 from the pipe line 3, said branch terminating in a jet in a slotted block 35. Opposite the jet is the inlet of apipe 36 connected to the bellows 32. The lower edge'of the blade.

26 moves in the slot of the block 35, and serves to control the passage of 'air from the pipe 34 to .the

pipe 36 and hence to the bellows. To the. top of the shaft 30 is fixed a worm 3'I driving a wheel 38 fast with a screwed shaft 39 on which is mounted the block 35. When the bellows 32. receives su'fiicient air to hold the friction ring .29 in contact with the disc 21 the shafts 30 and 39 a1 rotated and the block as is moved to the right until, owing to the curvature of the lower. edge of the blade 26,the air supply to the bellows is insufiicient to 4 hold the friction ring 29 against the disc 21. If

, the air supply to the bellows 32 is sosmall that the friction ring 29 is held against the disc 28, theparts will move in the reverseeirecuon until the bellows 32 expand against the action. of the spring Fast with the shaft 39 is a gear 40, which 33. drives through the. intermediary. of gearing, not shown in detail but indicated by the chain line M (Fig. 4) a gear 42 fast with a shaft 43 rotation 49 represents the height of the 'aircraft. .A pro-..

jection 5I0 on, a depending portion 'of the base plate 20engages with a cam 5 on the spindle I I, to which is secured the setting knob I0 previously described, so that rotation of the setting knob has the effect of varyin a datum in the' height mechanism by'rocking the base plate 20 on which the bellows I8, I9 are mounted and hence moving the blade 26.

Airspeed mechanism The air speed mechanism is similar in many;- respects to the height mechanism and comprisesv a bellows 58 connected to pitot pressure and a. bellows 59'connected to static pressure, said bel-Z lows being mounted upon a base plate 60, and the P tops of the bellows being connectedto' frames BI, 62, secured to 'pivoted'links63, 64, mounted on'a' spindle to which is secured a blade 66, the free end of which moves, in aslotted blockIS, similar I0, having a flexible coupling 'II and carrying .a friction ring I9, which mayj'engage with either I of a pair of friction discs 61', 68 driven by'th'e motor I; Theshaft drivesthroughxgearingj 11,';I8;a screwed shaft 19; along whichzthe block. moves to adjust the air supply to the bellows With increase in the airspeed the bellows 58 will expand causing the blade 80 to move and the shaft 19 consequently to rotate, in a manner similar to that describedfor the height'mechanism. A gear 80, secured to the shaft 19" drives through gearing, not shown in detail but indicated by the broken line 8|, a gear wheel 82 fast with a'shaft 83 which drives through gearing-84; 3'5, 06, a pinion 8'1 located between end stops 815, 81! and tapped to accommodate a screwed'shaft 88; R0- tationof the pinion 81 thus causes the shafttB- to move endwise carrying with it a carriage 89 which may be termed the drift carriage and the function 'of which will i be described hereinafter. Changes in airspeed are therefore'represented by lateraldisplaceinent of the shaft 38 and drift carriage 89.. To the drift carriage is attached a pointer 90, which moves over a scale 9'I engraved to indicate airspeed values. At the same time rotation of the pinion 81'causes a pinion 92 to rotate, said pinion 92 being prevented'by means not. shown from. lateral movement, and being tappedto receive a screwed shaft 93 to which is secured the carriage 5! carryingthe heightscrew 48 previously referred to. Thus variation in airspeed causes lateral displacement of the shaft es and carriage 51, and consequent resetting of the pivoted arm 50. The movement of the shaft 93 is however also controlled by the wind mechanism, as described hereinafmr, and its displacement represents not airspeed, but ground speed.

Wind mechanism The wind mechanism comprises a radially slotted pinion H0 driven from the shaft IOI through differential gearing 'IIi, H2, H3, H3, H5. A scroll pinion H3 is alsoprovided coaxial with pinion lit and driven from th'eshaft Iti through the gears Ii-I, I52, H3, lrl i, H1, H8, H9 and 29. The shaft I35 also drives the scroll pinion H6 through a compensating differential gearing IZI, I22, I23, H9 and i'2.0.-- The=course of the aircraft is'also fed into theidiiferential' gearing HI, Il2, ii3, H4, H5, from-the shaft"v I24, which may be rotated by a rcpeaterrnotor changeof course, the navigationalbearing of the:' pin I26,- relative to the axis of the'pinionsnl til and II 6, will be varied, while rotation ofithe knobx.

IM to preset a new wind speed, will cause the pinion H6 only to rotate and will alter only the distance between the axis of the pinions H0 and I I0 and the pin I26. Rotation of the courseshaft I24. also drives gearing I29, I39, causing adial. I3I to rotaterelative to a fixed pointer 32, the face of the dial being engraved to represent course.

The pin I281 is secured to a metal-tape I33at-' tached at itsother end to'a carrier I34- in which is" mounted the groundspeed shaft 93; A spring 200 (Fig. 4) attached to the'carrier I34 by rod 200- maintains tension in the tape I33. Thus rotation of the pinion 'IIE while pinion IIOis-' stationary causes the pin IZt'tobe moved along the slotin the latter and causes lateral displacee of the aircraft above the target.

a ment ofithe pin. I28; tape: I33; carrier I34'1and; ground speed shaft 93. The tape-J33: passes through rollers I35, I35 on a frame I31,.-piv0tedto. the shaft 88, havinga slottedarm I in the: slot of which the pin I28 is located. If the pinion H0 or bothpinions H0 and IIS are rotated the pin |283Wi11 undergo rotational or rotational and translational movement and may assume for example. the position indicated by broken lines e. g. at I28, the tape I33 moving to the position. shown at I33, and the slotted arm I38 moving; to I38. This will cause the tape I33 and ground; speed shaft 93 to take up a new position, and the pivoted frame I31 to be rotated, the result pro-, ducedby the latter movement being. described: underthe heading Drift Mechanism. The line; joining the pin I23 and the single axis of pinion IIO will thus represent the wind vector in the, diagram of Fig. 8, while the length of tape be-= tween the pin I28 and rollers Irepresents the groundspeed vector.

Drift mechanism Rotational movement of the pivoted frame- I31 causes movement of a blade J39 secured thereto in a slotted block H30, which blade variably obstructs the passage of compressed air from a pipe I41 communicating with the-pipe 3, to a pipe 142 feeding a bellows I43 (Fig, 4). pansion of the bellows Hi3 against the action of a return spring I l causes movement of a frame I45, carrying a shaft Hit-having a friction ring I31 which may engage with either of two friction discs I158, I 39 driven by the motor 2;

Rotation of the shaft 536 causes a shaft I to rotate through gearing ltl, I52, I53, the shaft I50 constituting the drift angle driv which is to be connected to the sighting arrangement. The blade I39 thus constitutes the detector of an electro-pneumatic servo system similar in general character td those in the height and airspeed mechanisms. The follow-up mechanism comprises a flexible shaft I543 driven from the shaft I50 through gearing 55, I56, I51, I53, I59, to the end of which is secured a screw Iiii'l fixed to the drift carriage 89 and on which is mounted the slotted block M0. 1

Bombing angle mechanism The carriage EE-l (Fig. 4.), described under the heading Height Mechanism, is secured to the shaft 93 and its lateral displacement therefore corresponds to changes in ground speed, while" the height of the nut 459' represents the height" Thear'm 53 is. secured to a pulley lil to which is securedone end of a tape F52 which is always maintained taut; consequently the arm 50 is always in contact with the projection on the nut cs andthe position of the arm always represents a vane for the ideal bombing angle as hereinbefore defined. The tape I62 passes round a floatingpulley I53 and is secured at its other end to a third pulley I0 3, which carries a second arm I35, the 05 function of which will be described subsequently. To the pulley I63 is secured a shaft H carrying one end of a variable fulcrum lever I61, whose fulcrum is a pin I63. To the other end of the lever I31 is secured a framework I69 on which is mounted a slotted block I10; working in the slot in the block is a blade Ill secured to a shaft [12f which is attached to the gimbal of a pitch gyro I13.

The blade I1I variably obstructs the ipassage'of air under pressure from the pipe '3 to a pip *I14 to-inflate a bellows I15, against the action of a return spring I16, and constitutes part of a further electro-pneumatic servo mechanism similar to such mechanisms already described. The bellows controls the position of a frame I11 in which is mounted a shaft I18 having a friction ring I19, which can make contact with either of two friction discs, I80, I8I driven by the motor 2. Movement of the blade I1I in response to a change in the pitchattitude of the aircraft, or of the block I10, due to movement of the floating pulley I63 and lever I61, is thus transmitted to the shaft I10, movement of which in turn is transmitted through gearing I82, I83, I84, I85 to a shaft I86 from which the sighting angle is transmitted to the sighting head- The follow-up mechanism comprises a pinion I81 on the shaft I86 engaging with a further pinion I88 whence the drive istaken through gearing not shown in detail but indicated by the broken line I89, to a pinion I90 on a shaft I9I and thence through gearing I92, I93, I94, to shaft I95 to which is secured a variable pitch screw I96 forming a cam groove and on which is mounted a nut I91 having a projection I90 engaging the arm I65 fixed to the pulley Thus movement of the shaft I86 is transmitted to the pulley I64, causing the tape I62 to be moved and to move the floating pulley I63 and lever I61 to move the blade 11! and block I13 into their equilibrium positions in which the air passing through block I from the pipe 3 to the. pipe I14 maintains the bellows I15 at such inflation that the friction ring I19 is held out of contact with the friction discs I80, I8I. Movement of the shaft I9I is also transmitted through gearing 20I, 202, 203 to a quadrant 204, carrying a cam plate 205 having a scale 206 engraved with values for the sighting angle, said scale being moved past a stationary pointer. The cam plate also has a cam shaped guide slot 201 embracing the fulcrum pin I68 for the lever I61.

The change in sighting angle with varying pitch attitude of the aircraft is not only dependent on the value of glide or climb but also on the actual value of the sighting angle, and the mechanism, just described provides a suitable means for correlating these values.

Trail mechanism The trail mechanism includes a three dimensional cam 265 (Fig. 3) which is rotated from the shaft 26I through gearing 266, 261, 268, 269, to actuate a pivoted follower 210 causing lateral displacement of the shaft I95 (Fig. 4), variable pitch screw I96, nut I91, arm I65 and thence through the pulley and tape mechanism already described to the sighting angle shaft I86. The cam is mounted to slide on the shaft 83 driven by the gear 82 in the air speed mechanism. Also mounted on the shaft 83 is a nut 21I which'is prevented from rotating so that when the shaft 83 is caused to rotate the nut 21I moves along it. Secured to the nut 21! is a frame 212 terminating in a fork embracing the gear 269 to which the cam 265 is fixed, so that the cam is moved endwise by rotation of the shaft 83. Thus movement of the cam follower 210 is governed both by air speed and by the terminal velocity of the bomb. Tables are available giving the relationship between trail distance and airspeed for bombs of differing terminal elocities dropped from varying operating heights. Thus the variation in effective radius of the cam as it is rotated corresponds with the known effect of varying the terminal velocity of the bomb while the taper of the cam in the longitudinal direction corresponds with the known effect of varying the airspeed on bombs of the same terminal velocity.

Sighting head A convenient form of sighting head is illus trated in Fig. 6, in which an inverted tripod 300 indicated in broken lines is pivotally mounted at 3! on a base plate 30I. Two legs 3I9, 320 of the tripod 300 are shown in the drawing. A worm 302 carried by the base plate 30I is driven by a flexible shaft from the drift angle shaft I50, see

Fig. 4, and engages a nut 303 having a pin 304 which passes through a slotted lug 305 fast with the tripod 300. Mounted on the tripod 300 is a casing 301 for a roll gyroscope whose outer gim Secured to the arm 3| I is a toothed quadrant 3 I4,.

engaging with a gearwheel 3I5 driven by a worm 3 I 6 and flexible shaft 3I1 from the sighting angle shaft I86, see Fig. 4.

Thu the sighting head is rotated in azimuth in response to changes in drift angle evaluated by the computer and transmitted through the shaft I50, while the collimator (H2 is tilted relatively to the screen 3I0 in accordance with changes in sighting angle evaluated by the computer and transmitted through the shaft I86. Accordingly, if the manual settings on the computer are correctly made and the computer is functioning correctly, a projectile released at any moment will strike the point viewed through the screen 3I0,

upon which the image of the graticule appears to be superposed at the instant of release.

We claim:

1. An aircraft bombsight comprising the combination of a computer including means for continuously computing the drift angle and means for continuously computing the ideal bombing angle and for applying a trail correction to said bombing angle and a further correction in re-' sponse to changes in pitch attitude of the aircraft to obtain continuously the value of the sighting angle, said last named means comprising a rotatable pulley, means for angularly positioning said pulley in accordance with changes in.

aircraft height and ground speed to represent an ideal bombing angle, a flexible element anchored at one end to said pulley, an adjustable anchorage for the other end of said flexible element, a mov-,- able member and means for adjusting the position of said member in accordance with the length of said flexible element between said pulley and anchorage, a movable element whose position is to represent the actual sighting angle, a coupling between said movable member and movable element, and means for adjusting said anchorage in accordance with the ballistic properties of the selected projectile, the aircraft air speed and the position of the movable element; an adjustable optical'sighting means for defining a sighting line; and transmission means between said computer and said sighting means for continuously,

transmitting the drift and sighting angle values so obtained to the sighting means so as to move the sighting line accordingly, whereby thepoin-t sighted at any moment is the point of impact of a bomb released at that moment.

2, An aircraft bombsight comprising the combination of a computer including means for continuously computing the drift angle and means for continuously computing the ideal bombing angle and for applying a trail correction to said bombing angle and a further correction in response to changes in pitch attitude of the aircraft to obtain continuously the value of the sighting angle, said last named means comprising a pulley, means forrotating said pulley to a position representing an ideal bombing angle, a second pulley, a flexible element having its ends anchored to said pulleys, a member movable in response to changes in the length of the flexible element between said pulleys, a lever movable by said member, a pitch gyroscope, a movable element whose position represents the actual sighting angle, a servo mechanism controlled by said lever and pitch gyroscope for adjusting the position of said element, and means for angularly positioning the second pulley in accordance with the ballistic properties of the selected projectile, the aircraft air speed and the position of the said element; an adjustable optical sighting means for defining a sighting line; and transmission means between said computer and said sighting means for continuously transmitting the drift and sighting angle values so obtained to the sighting means so as to move the sighting line accordingly, whereby the point sighted at any moment is the point of impact of a bomb released at that moment.

3. An aircraft bombsight comprising the combination of a computer including means for continuously computing the drift angle and means for continuously computing the ideal bombing angle and for applying a trail correction to said bombing angle and a further correction in response to changes in pitch attitude of the aircraft to obtain continuously the value of the sighting angle, said last named means comprising a pulley, means for rotating said pulley to a position representing an ideal bombing angle, a second pulley, a flexible element having its ends anchored to said pulleys, a member movable in response to changes in length of the flexible element between said pulleys, a lever movable by said member, a pitch gyroscope, a movable element whose position represents the actual sighting angle, a servo mechanism controlled by said lever and pitch gyroscope for adjusting the position of said element, means for angularl positioning the second pulley in accordance with the ballistic properties of the selected projectile, the aircraft air speed and the position of said element, said lever including a variable fulcrum, and means for adjusting said fulcrum in response to changes in the value of the sighting angle; an adjustable optical sighting means for defining a sighting line; and transmission means between said computer and said sighting means for continuously transmitting the drift and sighting angle values so obtained to the sighting means so as to move the sighting line accordingly, Whereby the point sighted at any moment is the point of impact of a bomb released at that moment.

4. An aircraft bombsight comprising the combination of a computer including means for continuously computing the drift angle and means for continuously computing the ideal bombing angle and for applying a trail correction to said bombing angle and a further correction in response to changes in pitch attitude of the aircraft to obtain continuously the value of the sighting angle, said last named means comprising a rotatable pulley, means for angularly positioning said pulley in accordance with changes in aircraft height and ground speed to represent an ideal bombing angle, a flexible element anchored at one end to said pulley, an adjustable anchorage for the other end of said flexible element, a movable member and means for adjusting the position of said member in accordance with the length of the said flexible element between said pulley and anchorage, a movable element whose position represents the actual sighting angle, a coupling between said movable member and movable element, and mechanism for positioning said movable element including a three-dimensional cam, manual means for moving the cam in one direction in accordance with the ballistic properties of the selected projectile, means for automatically moving said cam in another direction in response to changes in air speed and a follower on said cam for adjusting the position of said anchorage, thereby including a trail correction in the position of said movable element; an adjustable optical sighting means for defining a sighting line; and transmission means between said computer and said sighting means for continuously transmitting the drift and sighting angle values so obtained to the sighting means so as to move the sighting line accordingly, whereby the point sighted at any moment is the point of impact of a bomb released at that moment. PATRICK MAYNARD STUART BLACKETT. HENRY JOHN JAMES BRADDICK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,152,946 I-Iasburg Sept. 7, 1915 1,314,428 Pollen et a1 Aug. 26, 1919 2,105,147 Inglis Jan. 11, 1938 2,118,041 Estoppey May 24, 1938 2,371,606 Chafee et a1 Mar. 20, 1945 2,409,648 Van Auken et al. Oct. 22, 1946 2,428,678 Norden et al. Oct. 7, 1947 

